Electrostatic printer and positioning means for special articles



Dec. 5, 1967 D, 5 LONDAHL ET AL 3,356,020

ELECTROSTATIC PRINTER AND POSITIONING MEANS FOR SPECIAL ARTICLES 1 Filed April 4, 1966 5 Sheets-Sheet 1 I NVENTOR5 S. LONDAHL v 1 2 MARLlN A. SCHUELER wyafizwww Dec. 5, 1967 s, LONDAHL ET AL 3,356,020

ELECTROSTATIC PRINTER AND POSITIONING MEANS FOR SPECIAL ARTICLES Filed April 4, 1966 3 Sheets-Sheet 2 INVENTORS DICK EY S. LONDAHL BYMARLIN ASCHUELER a 1 m hww Dec. 5, 1967 11s. LONDAHL ET AL 3,356,020

- ELECTROSTATIC PRINTER AND POSITIONING MEANS FOR SPECIAL ARTICLES INVENTORS DICKEY S. LONDAHL MARL-iN ASCHUELER w. MW

United States Patent 3,356,020 ELECTROSTATIC PTER AND POSITIUNING MEANS FDR SPECIAL ARTICLES Dickey S. Londahl, Walnut Creek, and Marlin A. Schueler, Danville, Califi, assignor's to Unimark Corporation, San Ramon, Califi, a corporation of California Filed Apr. 4, 1%6, Ser. No. 539,871 6 Claims. (Cl. 101-44) much " CT 035' THE DHSCLOSURE This invention relates generally to an electrostatic printer and particularly to apparatus for positioning and carrying articles to and past a printing station, and insofar as the electrostatic printing is concerned, it relates to such printing in which the printing medium is electrostatically deposited upon the surface of each article from a point spaced from said surface by conducting dry printing powder across an air gap from a supply thereof onto said surface. The transfer of the medium through the air gap is effected by establishing an electrostatic field between the source of said powder and the object or article to be printed upon. Such electrostatic printing is generally along the lines described in US. Patent No. 3,081,698, issued Mar. 19, 1963, to Childress et al.

One of the objects of the invention is the provision of an apparatus for electrostatically imprinting symbols and/ or information on the surface of articles having a projection thereon by which the articles may be oriented and held in an oriented position for accurately printing such symbols and information in a predetermined position on each article. One of such types of articles is transistors, which may be quite small, but which must be clearly marked with the desired information, symbols, or both, to avoid what could be fatal mistakes if vital operations in certain apparatus were to entirely depend upon the articles being ciearly identified. Rubber stamping or typeprinting depends upon the wet ink being deposited on an article without running or smearing, and the surface on which the printing appears should be smooth and flat.

With the present invention, roughness of the surface on which symbols or other material is printed, is immaterial, and such surface may be convex, concave, or rippled, and the printing medium is dry and will adhere in position Without running or smearing at the printing step. Furthermore, there is no contact between the article and a printing screen or the like to cause smearing.

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Another object of the present invention is to provide an apparatus for electrostatically printing on articles such as transistors wherein the printing medium deposited on said articles may go through a preliminary fixing stage before being removed from the apparatus.

Yet another object of the present invention is to provide an apparatus for rapidly and accurately handling and electrostatically printing upon articles such as transistors wherein the medium used in the step of printing is in a dry, or at least a surface-dry powder responsive to a positive or a negative charge of electricity. The powder may be supplied in loose form or abraded from a solid block or stick.

It is still another object of the present invention to provide an apparatus for electrostatically printing upon small articles such as transistors, as one example, wherein the standard of clarity of such printing is maintained at a standard of clarity heretofore approximated only on articles of considerably greater size.

Other objects and advantages will be apparent from the description and the drawings. In the drawings, FIG. 1 is a partially sectioned, partially broken away front elevational view of the handling and printing apparatus of the present invention.

FIG. 2 is a fragmentary top plan view of the apparatus of FIG. 1.

FIG. 3 is a sectional view, partially broken away, of the drive train of the present apparatus, which view is taken substantially along line 3--3 of FIG. 1.

FIG. 4 is a fragmentary side elevational view of the printing head of the present invention, partly in section.

FIG. 5 is an enlarged fragmentary part elevational and part sectional View of the printing head shown in FIG. 4.

FIG. 6 is a greatly enlarged fragmentary top plan view of a support for an article, such as a transistor, at the transfer point, as seen in FIG. 7.

FIG. 7 is an enlarged fragmentary cross-sectional view of the holder of FIG. 6 and part of the receiving disc for the transistor shown in receiving position with the transistor shown in broken lines.

In general, the apparatus of the present invention is adapted to very accurately position miniature articles such as transistors beneath an electrostatic printing head and within the electrostatic field created around said head, at which point code numbers and other information such as the manufacturers name may be imprinted upon a surface of said article. After the printing medium has been deposited on the surface of said article it should be fixed on the article against being readily rubbed oif or distorted by contact with other such articles, clothing, or a finger. Therefore, incorporated in the machine is means for transferring the imprinted article without disturbing its position to a station at which the printing medium can be fixed prior to subjecting the imprinted articles to contact with foreign objects.

After the printing medium has been fixed the imprinted articles can be removed from the apparatus of the present invention and transferred to other stations, if desired, without danger of smearing.

More specifically, and referring first to FIG. 1, the drive train of the device or apparatus herein illustrated and described may be mounted within a cabinet generally designated 1 and having a base plate 2, sidewalls 3, and a top plate 4.

Secured to the outside of one of the sidewalls 3 is a motor 5 which may have a gear box 6 in operative connection therewith. Depending from gear box 6 (as seen in FIG. 1) is a driven shaft 9. Rigid on shaft 9 is a sprocket wheel 10 (FIGS. 1 and 3) which may be held in place by collar 11.

Sprocket wheel 10, on the outside of cabinet 1, is connected to a larger sprocket wheel 12, in the inside of cabinet 1, by sprocket chain 13. Sprocket wheel 12 is secured on the lower end of a vertically disposed shaft 14 for rotation therewith.

Shaft 14 extends upwardly from sprocket wheel 12 through a bearing block 16 which is securely fixed to the lower surface of a horizontally disposed partition plate 19 within cabinet 1. Vertical shaft 14 then extends upwardly through top plate 4 of cabinet 1 and through a bearing block 20 secured to the upper surface of top plate 4.

Above top plate 4 is the article handling and electro static printing means of the present invention. The article handling means primarily includes a pair of horizontally disposed rotating discs, one for positioning the articles to be printed upon beneath a printing head and the other for positioning the imprinted article at a fixing station.

The positioning disc, generally designated 21, (FIGS. 1, 2), is mounted for rotation on the upper end of a vertical disposed shaft 22, which shaft extends downwardly through a bearing block 23 secured to the upper surface of top plate 4 and then through top plate 4 into the interior of cabinet 1. The means for rotating shaft 22 and therefore moving positioning disc 21 will be described in conjunction with the description of the drive train.

Referring to FIGS. 1 and 2, mounted on the upper side of positioning disc 21, as by bolts 24 (FIG. 2), are four outwardly directed article positioners 25 (FIGS. 1, 2) which are equally spaced around the periphery of the upper surface of disc 21. Each positioner includes a lower plate 26 made of conductive material and an upper plate 29 made of magnetic material. Opening outwardly of each positioner 25 away from the center of disc 21 is a slot 30 (FIG. 2), the inner end of which terminates in both upper and lower plates 26, 29, (FIG. 6).

As best seen in FIG. 4, beneath the inner end of each plate 29 a bore 31 is formed in discs 21 into which may be inserted a permanent magnet 32. Magnet 32 is magnetically held in place by contact with the underside of the inner end of plate 29 and aids in positioning an article to be printed upon as will be described later in greater detail.

Equally spaced between each pair of positioners 25, and secured to the upper surface of disc 21, as by bolts 33 (FIG. 2) are upwardly directed brushes 34, the purpose of which is to clean printing screens, as will be described in conjunction with the operation of the present invention.

Positioning disc 21 is adapted to momentarily position an article to be printed upon beneath a printing head generally designated 35 (FIGS. 1, 2, 4). Printing head 35 is positioned above disc 21 and is secured to top plate 4 by means of a vertical post 36 which, in turn, is secured to a base plate 39 (FIG. 2). Base plate 39 is secured to top plate 4 by means of bolts 40 extending through slots 41 in said base plate, whereby said base plate, post 36, and printing head 35 are laterally movable a short distance toward and away from positioning disc 21.

Printing head 35 includes an upper hollow housing 42 which is open at both its upper and lower ends. Extending through the sidewalls of housing 42 near the lower open end thereof is a horizontally disposed shaft 43 which may be rotatably supported in said sidewalls by means of bushings, bearings or the like. Mounted on shaft 43 for rotation therewith between the sidewalls of housing 42 is a drum-type brush generally designated 44. Brush 44 includes an inner drum 45 (FIG. 5) around the peripheral surface of which may be secured a brush portion 46 in any of several forms including bristles, tufted fabric, or a plastic-type foam. Most of brush 44 is enclosed within housing 42, however, the lower end of said brush extends downwardly out of the open lower end of said housing.

A powder hopper 47 is positioned within housing 42, which hopper may be of any suitable shape or arrangement for supporting the printing medium and for depositing it on the brush 44.

In the example shown in FIGS. 2, 4 this hopper 47 may comprise a pair of opposed sidewalls 48 adjacent two of the opposed sidewalls of housing 42, and vertically removable from the upper end of housing 42. A pair of spaced opposed vertical walls 49 secured between walls 48 spaced between the vertical edges of walls 48 cooperate with said walls 48- to form a central vertical passageway of rectangular cross sectional contour within which a vertically disposed stick P (FIG. 2) of compacted, readily abradable pigment is vertically slidable for being supported at its lower end on the upper side of brush 44. Screws 48' extending through one of the sides of housing 42 may, if desired, engage one of the walls 48 of the hopper for supporting the lower edges of walls 49 approximately against the upper surface of brush 44, although the hopper may rest on the brush, and may be relatively loose insofar as its movement transversely of the planes of walls 49 is concerned, so that it may move slightly as brush 44. is alternately rotated in one direction and the other, as will later appear. As the brush 44 rotates, the lower end of stick P is abraded to deposit powder or pigment on the brush, and the particles of pigment so abraded are sufficiently small to pass through the openings in a printing screen, later described, for passing through said openings.

It is obvious that loose powder may be fed to the brush from hopper 47 or any other suitable powder feed, and in such a case, screws 48 would not be used since a vibration of the hopper to preclude bridging of the powder would be desirable.

Shaft 43, and therefore drum brush 44, is rotated by shaft 14. Secured to the end of shaft 43 nearest to shaft 14 is a vertically disposed clutch disc 50. Mounted onshaft 14 for rotation therewith are a pair of horizontally disposed annular plates 51 and 52, plate 51 being sub-- stantially aligned with the top of clutch disc and plate 52 being substantially aligned with the bottom of clutch disc 50 with the plates 51, 52 being in planes at right angles to the vertical plane of disc 50. Formed in the peripheral edge of each plate 51, 52 is a recess adapted to receive an elastic O-ring 53. The O-rings 53 each have a projection 54, thereon with projection 54 being on the upper O-ring 53 and projection 55 being on the lower ring 53, said projections being adapted to frictionally engage the vertical surface of clutch disc 50, facing the plate 51, 52 at points above and below shaft 43.

Assuming plates 51 and 52 are being rotated in a clockwise direction as indicated by the arrow in FIG. 2, when the projection 54 engages the laterally facing surface of clutch disc 50, shaft 43 and drum brush 44 will be rotated in a counterclockwise direction as seen in FIG. 4 for the duration of such engagement. When the projection 55 (FIG. 2) on plate 52 engages clutch disc 50, shaft 43 and drum brush 44 will be rotated in the opposite: direction, or in a clockwise direction as seen in FIG. 4,, for the duration of such engagement. Thus, it can be seen that drum brush 44 is alternately rotated in both counterclockwise and clockwise directions beneath the imprinting medium in hopper 49 upon alternate contact of projections 54, 55 with disc 50. By making the projection 54 on plate 51 annularly longer than the projection 55 on plate 52 brush 44 will be rotated farther in a counterclockwise direction than in a clockwise direction as seen in FIG. 4. Thus, upon each actuation of brush 44 a net advance in a counterclockwise direction will be effected and a part of a brush portion 46 of said brush containing a fresh supply of imprinting medium will be made available for each printing operation.

Housing 42 is adjustably mounted on post 36 for ver tical movement toward and away from disc 21. Such mounting may be accomplished by means of a pressure or clamping plate 56 slidably received within housing 42 and projecting rearwardly from which are a pair of bolts 57. Bolts 57 pass from pressure plate 56 through vertical slots in an endwall of housing 42 and then through bores in post 36 and are secured by wing nuts 58 that are adapted to engage the side of post 36. When wing nuts 58 are tightened against post 36 on bolts 57 the pressure plate 56 clamps the endwall of housing 42 against post 36 thereby holding the housing in adjusted position. When wing nuts 58 are loosened, housing 42 is capable of being moved vertically a slight distance toward and away from disc 21.

To assure accurate control of this movement of housing 42, a bar 59 is secured across the top of the sidewalls of housing 42, at the rear thereof, where said sidewalls laterally lap post 36. Extending downwardly through a bore centrally of bar 59 is a bolt 66' the lower end of which is screw threadedly received in the top of post 36 and around bolt 60 is a coil spring 63 which reacts between said bar and the top of said post for continually urging housing 42 upwardly.

When wing nuts 58 are loosened, housing 42 is accurately moved upwardly or downwardly by the rotation of threaded bolt 60. Spring 63 assures that there is no slack in the movement of housing 42 and that it remains in the selected position while wing nuts 58 are again tightened.

Also mounted on post 36 and interposed between housing 42 and disc 21 is a printing screen housing 64. Screen housing 64 is adjustably mounted on post 36 for movement toward and away from disc 21 in much the same manner as is housing 42. Screen housing 64 includes a removable screen holder 65 secured across the open lower end thereof which holder holds an inter changeable printing screen 66. Screen 66 may be secured to the lower side of a frame 67 (FIG. that is slidable in opposed grooves 68 in holders 65.

Screen housing 64 is adapted and positioned to receive the lower end of drum brush 44 in the open upper end thereof. The lowest point of the brush portion 46 of drum brush 44 is adapted to engage the upper surface of screen 66 the purpose of which will be explained in detail in conjunction with the operational cycle of the present invention.

The sides of drum 44 may be closed by vertical side plates 67 that, in turn, may fit relatively close to the inner opposed sides of the upper drum housing 42 and the sides of the printing screen housing. Also clamping of pressure plate 56 continues downwardly to engage the end wall of housing 64 that is below the end wall of housing 42 thereabove. A bolt 68 (FIG. 4) secured at one end to the lower portion of clamping plate 56 extends through a vertical slot in the end wall 69 and then through a hole in the post 36, in the same manner as described with respect to bolts 57. A wing nut 70 clamps housing 64 in adjusted vertical position.

Mounted above plate 4 and in cooperative relationship to positioners 25 of printing disc 21 is a print fixing disc 73 (FIG. 2). Disc 73 is mounted on a vertically disposed shaft 74 (FIG. 1) for rotation therewith which shaft extends downwardly through a bearing block 75 secured to top plate 4 and then through said plate into the interior of cabinet 1. Disc 73 'is of substantially the same thickness as and is elevationally aligned with the lower plate 26 of positioners 25. Print fixing disc 73 has a plurality of outwardly opening slots 76 (FIG. 2) formed in the periphery thereof, which slots are adapted to be aligned with the slots 30 of positioners 25 on printing disc 21.

The means for so aligning slots 76 and 30 will be thoroughly described in connection with the description of the drive train of the presentinvention.

Mounted on the upper surface of the top plate 4 and substantially intermediate the shafts 22 and 62 is a transferring device generally designated 77 (FIG. 1) which is adapted to transfer printed articles from the printing disc 21 to the print fixing disc 73.

Transfer mechanism 77 includes an upstanding bracket 78 which is secured to the top plate 4 and through an aperture in the upper end of which extends a horizontally disposed rod 79. Rod 79 may be held in place with respect to bracket 78 by a pair of collars 80 secured to rod 79 on opposite sides of bracket 78.

Secured to one of the collars 80 and extending generally upwardly therefrom is an arm 83 having a right angle extension 84 at its upper end that is adjacent to the lower side of lower plates 26 of positioners 25 and which extension is adapted to be yieldably urged against the peripheral edge of disc 21 by any suitable means, such as a torsion spring 84 connecting bracket 78 and one of collars 80 (FIG. 2).

On the end of rod 79 opposite to arm 83 is secured a camming member 86. Camming member 86 projects generally radially and upwardly from rod 79 and its upper side is adapted to be engaged by a finger 87 which is secured to shaft 14 and projects radially therefrom (FIGS. 1, 2). As finger 87 is carried around by rotating shaft 14, said finger will engage the upper side of camming member 86 forcing said member downwardly and thereby cranking arm 83 and its extension 84 to the left as seen in FIG. 1. When finger 87 has passed the camming member 86 said extension 84 is again yieldably urged into engagement with the peripheral edge of disc 21.

Actuation of transfer mechanism 77 is timed in relation to the rotation of discs 21 and 73 and it can be seen that the printed article which may be in the slot 30 of positioners 25 would be moved out of said slot and into an aligned slot 76 of disc 73 upon actuation of the transfer mechanism.

A horizontally disposed heating element 88 is adjustably positioned above print fixing disc 73 and is supported in place by an upstanding bracket 89 which is in turn secured to top plate 4. The heat. generated by heating element 88 fixes the printing medium on the surface of an imprinted article.

Most of the driving and timing mechanism of the apparatus is positioned within cabinet 1, and between partition 19 and top plate 4 (FIG. 1). In FIG. 3, the parts shown in FIG. 1 between partition 19 and top plate 4 are separate from the cabinet.

Shaft 14 is continually rotated in one direction through its sprocket chain connection with the shaft 9 that, in turn, is driven by motor 5. Said shaft 14 is the one that carries upper and lower clutch discs 51, 52. An arm 90 (FIGS. 1, 3) is secured at one end thereof to shaft 14 and projects radially outwardly of the latter. A roller 93 is carried by the outer end of arm 90 and projects upwardly therefrom. Immediately above arm 90 is a generally crescent shaped locking wheel 94 providing a circular outer peripheral edge 95 interrupted by a concavely curved linearly extending section 96. Arm 90 is positioned to cross the downwardly projected outline of edge section 96 substantially midway between the ends of said section.

Shaft 22, to which the article positioning disc 21 is secured, is parallel with and spaced from shaft 14 (FIG. 1) and has quarter-turning wheel 97 secured thereto. Wheels 94, 97 and the arm 94 including roller 93, provide a Geneva movement or Geneva stop. Wheel 97 is formed with four equally spaced linearly concave, circularly extending edges 98 each being complimentary to the linearly extending convex circular edge 95 of wheel 94, and between the ends of adjacent pairs of said edges 98 are radially extending slots 99 adapted to receive roller 93 when wheel 97 is locked stationary by edge 95 being in a concavity or hollow provided by one of the edges 98. With each full rotation of shaft 14, the wheel 97 will be rotated a quarter turn, and the arrangement is such that between movements of the wheel 97 one of the four article positioners will be stationary below screen 66, and also slot 30 in the positioner 25 ahead of the positioner that is below screen 66 will be in alignment with a slot 76 in the print fixing disc 7 3'.

It is not intended that the Geneva movement provided by this structure be restricted to move wheel 97 or more nor less than quarter turns with each revolution of the shaft 14, since anyone skilled in the art may modify the structure so that the wheel 97 may make more or less than such quarter turn, with each such full revolution, thus providing for positioning more or less than four articles on positioning wheel 90.

Secured on shaft 22 above wheel 97 is sprocket wheel 100, and a sprocket chain 103, connects chain 103 with a larger sprocket wheel 104 that, in turn, is secured on the lower end of shaft 74. Shaft 74 has the printing disc 73 on its upper end.

The differences between the sizes of sprocket wheels 100, 104, in the present illustration, are such that the print fixing disc 73, which is on shaft 74 will make only onetwelfth of a full revolution upon a quarter revolution of disc or wheel 97, but each slot 76 in wheel 73 will be aligned with the slot 30 in each positioner 25 on disc 21 with each quarter turn of the latter.

In FIGS. 4, 6, 7 a conventional transistor body is indicated at 105, and each such body has elongated wires 106 similarly projecting from one side thereof. In operation the body 105 of a transistor is positioned on each positioner 25 so that wires 106 depend from the body through slot 30 in each positioner. These transistors incorporate magnetic material, and each body 105 has a flat surface, which may be called a bottom surface, from which the wires extend, and which surface is perpendicular to the wires or conduits 106. In some transistors a flange 107 (FIGS. 6, 7) is formed around the transistor adjoining the flat bottom surface thereof.

As seen in FIGS. 6, 7, the lower and upper plates 26, 29 are each formed with a laterally opening V 30' at the bottom or closed end of each slot 30. This may be large or small, but where, as in the example, the transistors are cylindrical, this V functions to accurately center the transistor relative to the plates 26, 29. The lower plate 26, while electrically conductive, is preferably not magnetic, while the upper plate 29 is magnetic, the latter being held against the lower plate 26 solely by a permanent magnet 31, which, in turn, functions to magnetically hold the body 105 of each transistor against the sides of the V at the inner end of each slot 30 until the transistor is moved away from plate 29 longitudinally of each slot.

Once during each rotation of shaft 15 the finger 87 thereon will engage the upwardly inclined arm 86 that is on the rod 79, thereby rotating said rod to swing the right angle horizontally extending extension 84 thereon counterclockwise, as viewed in FIG. 1, with the result that said extension will engage the depending wires 106 on a transistor when slots 30, 76 are in alignment, thereby moving the transistor from positioning disc 21 onto the print fixing disc 73, with wires 106 depending through a slot 76 in disc 73.

There is a tendency for the extension 84 to swing wires 106 upwardly when the extension engages the wires 106 therefore a stationary, vertical stop plate 108 below each slot 76 at the transfer point will engage the lower ends of the wires and as the extension 84 continues its swing to broken line position 84' (FIG. 6) the wires 106, as indicated in dotted lines 106' in FIG. 6, will swing back to vertical and the transistor body 105 (dotted line position) will be in a predetermined position on the print fixing disc for being carried below the print fixing device 88.

Obviously the transistor may be manually removed after the printing is fixed, or any suitable stationary arm 109 may extend angularly across the upper surface of disc 73 at a point between the transfer point between discs 21, 73 and the print fixing device 88 for automatically sliding the transistors off the disc 73 and onto any suitable collector or conveyor therebelow for removal, and any further processing that may be deemed to be desirable.

It is to be noted in FIG. 6 that the magnetic plate 29 of the article positioner may be recessed or rabbetted at 110 to receive the flange 107 on the transistor where such flange exists. Some transistors and articles of generally similar shape do not have such a flange, but the provision of such recess in no manner alters the efliciency of the positioner where there is no flange.

The screen 66 may be either of woven material or perforated sheet material. The mesh openings or perforations may be quite fine, such as from 300 and more per inch, since the diameter of the top of each body may be less than one-eighth of an inch and may have fifteen or more numerals, letters or symbols thereon that must be clearly legible under a magnifying glass. The upper surface of each body 105 may be flat, convex, concave, dimpled or corrugated, or of other irregular character, yet the printing will be accurate and clear since there is no contact between the screen and the article.

A conductor, such as a flat spring 111 (FIG. 4), is positioned to make wiping contact with a nut 24' on the lower end of each bolt 24 at the point where each positioning device is in printing position below screen 66, and a conductor 112, electrically insulated from conductor 111 (FIG. 2) is in wiping engagement with the shaft 43 that carries the brush 44, which brush, in turn, is in contact with the printing powder and screen 66 at all times. By

- this arrangement a DC electrical potential differential is established between each article or transistor and the powder screen 66. Either electrode or conductor may be grounded according to the characteristic of the printing powder, so that the powder will be drawn from the screen into the electrostatic field established between the article and the screen for deposit onto the article in a pattern that corresponds to the pattern of openings in the screen. The electrostatic printing step itself is substantially as described in the Childress Patent No. 3,081,698.

The brushes 34 on the positioning disc 91 function to wipe surplus powder from the lower side of screen 66 after each printing operation so as to keep the screen clean, while the rotary brush 44 forces powder through the screen openings during each printing step.

It has been noted that the clutchv mechanism including the projections 54, 55 on the O-rings around circular plates 51, 52 function to reciprocate the brush portion 56 on brush 44 to a greater degree on each alternate movement, thereby progressively applying a new powder laden portion of the brush to the screen with each reciprocatory movement.

From the foregoing description it is seen that broadly the apparatus described comprises a turret rotatable about a vertical axis, but having means for supporting and positioning alticles thereon for movement in one direction in an annular horizontally disposed path about said axis and successively to and past a printing station at a point around said path upon rotation of said turret, a powder supporting printing screen is positioned over I said path at said station in spaced opposed relation to articles carried therepast by said turret, and means is provided at said point for establishing an electrostatic field between each article and said screen at said point when each article is in said spaced opposed relation to said screen for thereby conducting powder from said screen onto said article.

Such a turret enables providing a convenient feed station and discharge station at other points around said path at opposite sides of said printing station, each readily accessible to a single operator stationarily positioned alongside the turret.

Whether the turret is a horizontal plate or spider arms extending radially outwardly from said axis is, of course, immaterial.

In actual practice in a particular operation the stencil screen having the pattern of unobstructed openings corresponding to the desired letters, symbols, etc. to be printed is placed in the screen supporting bracket or holder 65, in which position it is horizontal and there is nothing between it and the article to be printed upon.

An article to be printed upon may then be positioned on one of the article positioning devices 25 of the turret or positioning disc 25. The turret may then be rotated so that the upper surface is in direct spaced opposed relation to the pattern of unobstructed openings of screen 66, so that the powder on the screen will be deposited in exactly the desired position on the surface of the article when a proper electrostatic field is established between the screen and said surface.

The screen can readily be moved laterally and vertically to an adjusted position so that the highest degree of accuracy and efficiency may be obtained. Provision has been made for said movements of the screen, as has been described in detail.

In this connection where, as in the example, the body of a transistor is small and cylindrical, its upper surface is circular, and it may be desirable to print an annular row of numbers and letters or symbols on the annular marginal surface of said upper surface, with other symbols in the center, and different lots of articles may be of diiferent diameters with different symbols to be printed thereon, and they may be of difierent vertical thicknesses. Thus the screen may require changing and adjusting both vertically and laterally, and the position of the article must be positioned with highest accuracy, or part of the printing may entirely miss the article, or be so badly distorted as to be unreadable.

An error in marking a part may be disastrous where said part is to be used as a critical element in a control unit and reliance is placed upon identifying symbols printed on the article.

While the present invention is illustrative of a system for marking transistaors, it is obvious that it is adapted for marking any article having a head and a projection, stem or other means thereon by which the article may be oriented or held in a predetermined position relative to the printing screen, and anyone skilled in the art may readily adapt the system to electrostatically printing on articles successively moved past a printing station irrespective of the shape of the article or the existence of a projection thereon. Accordingly, the invention is not to be limited to the specific example described, but is intended to cover any modifications and changes that may come within the scope of the following claims.

We claim:

1. In the method of electrostatically printing on articles of uniform size, shape and contour that includes supporting a printing powder on one, stationary horizontally disposed printing screen having openings therein through which said powder is adapted to pass into an electrostatic field below said screen for being conducted onto such articles;

(a) supporting the articles to be printed upon for movement in a substantially horizontally disposed annular path to and past a printing station and holding said articles centered in said annular path against movement radially and axially of said path during said movement to and at said printing station;

(b) supporting said screen stationary spaced a uniform distance above said path at said printing station with said screen in spaced opposed relation to each article therebelow in said path upon each article being moved to said printing station;

(c) moving articles so supported in one direction in said annular path to said printing station without changing their positions in said path or relative each other and without movement about their respective axes to successively pass said screen in spaced opposed relation to said screen;

(d) establishing an electrostatic field between said screen and each article upon each article being moved to said printing station and in said spaced opposed relation to said screen.

2. In the method of electrostatically printing on articles that includes supporting a printing powder on a horizontally disposed printing screen having openings therein through which said powder is adapted to pass into an electrostatic field below said screen for being conducted onto such articles;

(a) supporting the articles to be printed upon for movement in a substantially horizontally disposed annular path to and past a printing station;

(b) supporting said screen spaced a uniform distance above said path at said printing station with said screen in spaced opposed relation to each article in said path upon each article being moved to said printing station;

(c) moving articles so supported in one direction in said annular path without changing their positions relative to each other or their respective axes to successively pass said screen in spaced opposed relation to said screen;

(d) establishing an electrostatic field between said screen and each article upon each article being moved to said printing station and in said spaced opposed relation to said screen;

(e) said movement of said articles being intermittent between stationary stops thereof of uniform duration at said printing station;

(f) removing each article from said path after it has been moved to and past said printing station and said pattern of powder has been deposited thereon, and during the period between an intermittent movement of said articles in said path, and thereafter (g) fixing on the article so removed the powder electrostatically deposited thereon at said printing station;

1 h) supporting each article for movement in a second annular path extending tangentially away from said first mentioned annular path and substantially in the same plane of the path after each article has passed said printing station and the said step of fixing said powder on each article being at a point along said second path;

(i) and transferring each article from said first mentioned path to said second path and supporting each article in said plane during such transfer.

3. Apparatus for electrostatically depositing printing powder in a predetermined pattern onto articles, which apparatus includes a single horizontally disposed printing screen having a plurality of openings formed therein defining said pattern for passage of said printing powder through said openings for deposit onto said articles;

(a) conveyor means comprising a turret supported for rotation about a vertical axis having an annular row of equally spaced article supports rigid with and stationary on said turret equally spaced from said axis and disposed in a horizontal plane for movement in an annular path coaxial with said axis for supporting articles thereon, by gravity, and for lateral movement of said articles off said supports radially outwardly thereof when released for such lateral movement, and means on said turret for releasably holding articles stationary thereon in a precise uniform position for movement to a position spaced below said screen in opposed relation to the latter;

(b) a screen support for supporting said screen stationary over said path at a point along the latter,

(c) means for establishing an electrostatic field between each article and said screen when each article is supported on one of said article supports in said spaced opposed relation to said screen;

((1) powder supply means for supplying powder to said screen for passage through said openings and into said electrostatic field for deposit onto each of such articles,

(e) turret actuating means connected with said turret for rotating the latter about its axis in one direction, and

(f) powder moving means above said screen for moving powder from said powder supply means through the openings in said screen and into said electrostatic field when the latter is established.

4. In apparatus as defined in claim 3,

(g) said article supports each including a horizontally disposed plate on which one of said articles is adapted to be supported for said lateral movement radially outwardly of, and otf each plate relative to the vertical axis of rotation of said turret, said plate including a slot extending radially of said axis open at its radially outer end and provided with an article-engaging member at its inner end for respectively guiding an article to said inner end and for engagement with said member at said inner end and means for releasably holding each article in a uniform position on each plate against said member and movement radially outwardly thereof during movement of said article supports to said printing station.

5, Apparatus for electrostatically depositing printing powder in a predetermined pattern onto articles, which apparatus includes a horizontally disposed printing screen having a plurality of openings formed therein defining said pattern for passage of said printing powder through said openings for deposit onto said articles;

(a) conveyor means for supporting a row of said articles for movement in one direction along an annular path of travel extending below and past said screen, said conveyor means including article supports thereon in a row, each article support being adapted to support one of such articles thereon for movement therewith along said path and to a position in spaced opposed relation to said screen upon actuation of said conveyor for moving the latter, and conveyor actuating means connected with said conveyor means for actuating the latter for said movement thereof;

(b) a screen support for supporting said screen stationary over said path at a point along the latter;

(c) means for establishing an electrostatic field between each article and said screen when each article is supported on one of said article supports in spaced opposed relation to said screen;

(d) powder supply means for supplying powder to said screen for passage through said openings and into said electrostatic field for deposit onto each of said articles;

(e) powder moving means above said screen for moving powder from said powder supply means through the openings in said screen and into said electrostatic field when the latter is established;

(f) said conveyor means comprising a turret including a horizontally disposed first disc supported for rotation about a vertical axis, and said article supports being on said disc equally spaced from said axis in a row coaxial with the latter;

(g) said article supports being around the outer edges of said first disc and each including article positioning means for supporting one of said articles of the same shape and size, each having a main body with a projection on one side and a print receiving surface on the opposite side;

(11) a horizontally disposed second disc substantially 12 coplanar with said first disc and adjacent to the latter;

(i) means supporting said second disc for rotation about a vertical axis;

(j) article supporting means around the outer edges of said second disc in spaced relation in an annular row coaxial with said axis of rotation of said second disc;

(k) said article positioning means on said first disc and said article supporting means on said second disc including radially outwardly opening slots respectively provided on said first and second disc around the outer peripheries thereof for receiving the projection on each article through the open end of each slot with the main body of each article supported on the portions of the slots along the opposite edges of each slot upon such projections being inserted into said slots;

(1) means connecting said conveyor actuating means with said second disc for rotating said first disc and said second disc in synchronism for successively positioning each slot in said first disc in alignment with each slot in said second disc for lateral movement of articles on said first disc onto said second disc with the projection on each article movable from a slot in said first disc into a slot in said second disc in such alignment therewith;

(m) means for so moving each article from said first disc to said second disc; and

(n) fixing means over the outer marginal edge of said second disc for fixing the powder on the upper surface of each article onto the latter.

6. Apparatus for electrostatically depositing printing powder in a predetermined pattern onto articles, which apparatus includes a planar printing screen having a plurality of openings formed therein defining said pattern for passage of said printing powder through said openings and onto articles spaced from one side of said screen,

(a) conveyor means for supporting a row of said articles for movement in one direction along a path of travel extending to and past a point uniformly spaced from said one side of said screen and in opposed relation to the pattern of openings in said screen;

(b) a support for said screen supporting said screen in a position with said one side of said screen uniformly spaced from and in said opposed relation to said conveyor means at said point;

(c) said support including means for moving said screen to adjusted positions toward and away from said point and laterally relative to the latter and for holding said screen in any of said adjusted positions whereby powder passing through the openings of said pattern will be deposited on articles on said conveyor means at said point with extreme accuracy;

(d) means for supplying powder to the opposite side of said screen relative to said one side;

(e) means for establishing an electrostatic field between said screen and an article on said conveyor means at said point, and

(f) said conveyor means including a row of article positioning means movable therewith, each adapted to support an article at said point in uniformly spaced opposed relation to said screen;

(g) said means for supplying powder to said opposite side of said screen including a cylindrical brush supplied for revolution about its axis with one side thereof in Wiping engagement with said opposite side of said screen having the portion having said openings therein,

(h) means connected with said brush for alternately rotating it predetermined distances less than a full revolution in opposite directions upon movement of the article positioning means of each adjacent pair 13 thereof in said row to and past said point, and for moving said brush a greater distance in one 01': said opposite directions than the other, whereby a fresh surface of said brush will be progressively in contact with said screen a plurality of times during each full revolution of said brush.

References Cited UNITED STATES PATENTS 2,067,949 1/1937 Roz.

2,429,496 10/ 1947 Sutter 101-44 X 2,484,671 10/1949 Bauman.

2,935,933 5/1960 Moeller 101-44 14 Westervelt et al. 118-637 Childress et al. 101-129 Childress. Childress. Morgan. Usko et al 101-129 X Lusher. Childress et al. Schueler. Edwards et al.

ROBERT E. PULFREY, Primazy Examiner.

E. S. BURR, Assistant Examiner. 

5. APPARATUS FOR ELECTROSTATICALLY DEPOSITING PRINTING POWDER IN A PREDETERMINED PATTERN ONTO ARTICLES, WHICH APPARATUS INCLUDES A HORIZONTALLY DISPOSED PRINTING SCREEN HAVING A PLURALITY OF OPENINGS FORMED THEREIN DEFINING SAID PATTERN FOR PASSAGE OF SAID PRINTING POWDER THROUGH SAID OPENINGS FOR DEPOSIT ONTO SAID ARTICLES; (A) CONVEYOR MEANS FOR SUPPORTING A ROW OF SAID ARTICLES FOR MOVEMENT IN ONE DIRECTION ALONG AN ANNULAR PATH OF TRAVEL EXTENDING BELOW AND PAST SAID SCREEN, SAID CONVEYOR MEANS INCLUDING ARTICLE SUPPORTS THEREON IN A ROW, EACH ARTICLE SUPPORT BEING ADAPTED TO SUPPORT ONE OF SUCH ARTICLES THEREON FOR MOVEMENT THEREWITH ALONG SAID PATH AND TO A POSITION IN SPACED OPPOSED RELATION TO SAID SCREEN UPON ACTUATION OF SAID CONVEYOR FOR MOVING THE LATTER, AND CONVEYOR ACTUATING MEANS CONNECTED WITH SAID CONVEYOR MEANS FOR ACTUATING THE LATTER FOR SAID MOVEMENT THEREOF; (B) A SCREEN SUPPORT FOR SUPPORTING SAID SCREEN STATIONARY OVER SAID PATH AT A POINT ALONG THE LATTER; (C) MEANS FOR ESTABLISHING AN ELECTROSTATIC FIELD BETWEEN EACH ARTICLE AND SAID SCREEN WHEN EACH ARTICLE IS SUPPORTED ON ONE OF SAID ARTICLE SUPPORTS IN SPACED OPPOSED RELATION TO SAID SCREEN; (D) POWDER SUPPLY MEANS FOR SUPPLYING POWDER TO SAID SCREEN FOR PASSAGE THROUGH SAID OPENINGS AND INTO SAID ELECTROSTATIC FIELD FOR DEPOSIT ONTO EACH OF SAID ARTICLES; (E) POWDER MOVING MEANS ABOVE SAID SCREEN FOR MOVING POWDER FROM SAID POWDER SUPPLY MEANS THROUGH THE OPENINGS IN SAID SCREEN AND INTO SAID ELECTROSTATIC FIELD WHEN THE LATTER IS ESTABLISHED; (F) SAID CONVEYOR MEANS COMPRISING A TURRET INCLUDING A HORIZONTALLY DISPOSED FIRST DISC SUPPORTED FOR ROTATION ABOUT A VERTICAL AXIS, AND SAID ARTICLE SUPPORTS BEING ON SAID DISC EQUALLY SPACED FROM SAID AXIS IN A ROW COAXIAL WITH THE LATTER; (G) SAID ARTICLE SUPPORTS BEING AROUND THE OUTER EDGES OF SAID FIRST DISC AND EACH INCLUDING ARTICLE POSITIONING MEANS FOR SUPPORTING ONE OF SAID ARTICLES OF THE SAME SHAPE AND SIZE, EACH HAVING A MAIN BODY WITH A PROJECTION ON ONE SIDE AND A PRINT RECEIVING SURFACE ON THE OPPOSITE SIDE; (H) A HORIZONTALLY DISPOSED SECOND DISC SUBSTANTIALLY COPLANAR WITH SAID FIRST DISC AND ADJACENT TO THE LATTER; (I) MEANS SUPPORTING SAID SECOND DISC FOR ROTATION ABOUT A VERTICAL AXIS; (J) ARTICLE SUPPORTING MEANS AROUND THE OUTER EDGES OF SAID SECOND DISC IN SPACED RELATION IN AN ANNULAR ROW COAXIAL WITH SAID AXIS OF ROTATION OF SAID SECOND DISC; (K) SAID ARTICLE POSITIONING MEANS ON SAID FIRST DISC AND SAID ARTICLE SUPPORTING MEANS ON SAID SECOND DISC INCLUDING RADIALLY OUTWARDLY OPENING SLOTS RESPECTIVELY PROVIDED ON SAID FIRST AND SECOND DISC AROUND THE OUTER PERIPHERIES THEREOF FOR RECEIVING THE PROJECTION ON EACH ARTICLE THROUGH THE OPEN END OF EACH SLOT WITH THE MAIN BODY OF EACH ARTICLE SUPPORTED ON THE PORTIONS OF THE SLOTS ALONG THE OPPOSITE EDGES OF EACH SLOT UPON SUCH PROJECTIONS BEING INSERTED INTO SAID SLOTS; (L) MEANS CONNECTING SAID CONVEYOR ACTUATING MEANS WITH SAID SECOND DISC FOR ROTATING SAID FIRST DISC AND SAID SECOND DISC IN SYNCHRONISM FOR SUCCESSIVELY POSITIONING EACH SLOT IN SAID FIRST DISC IN ALIGNMENT WITH EACH SLOT IN SAID SECOND DISC FOR LATERAL MOVEMENT OF ARTICLES ON SAID FIRST DISC ONTO SAID SECOND DISC WITH THE PROJECTION ON EACH ARTICLE MOVABLE FROM A SLOT IN SAID FIRST DISC INTO A SLOT IN SAID SECOND DISC IN SUCH ALIGNMENT THEREWITH; (M) MEANS FOR SO MOVING EACH ARTICLE FROM SAID FIRST DISC TO SAID SECOND DISC; AND (N) FIXING MEANS OVER THE OUTER MARGINAL EDGE OF SAID SECOND DISC FOR FIXING THE POWDER ON THE UPPER SURFACE OF EACH ARTICLE ONTO THE LATTER. 